Question

Question 4. a) By analysing the Figure Q4 below describe the failure mechanism and how you came to those conclusions. 101

Answer 1

Answer: This a typical failure mechanism for a metallic materials i.e. consists of crack initiation followed crack propagation then catastrophic failure (without warning) as shown in figure below.

As shown in the figure above, due to applied external load (typically fatigue loading), first crack is nucleated at the edge and when it becomes critical crack then its started growing leads as shown as crack propagation region. The crack propagation region is indetified with the sign of striation (which crack leaves on the fractured surafce while it has moved ahead). Finally a stage came when this crack is not controllable and thus leads to catastrophic faliure (sudden failure).

Fatigue Striation Marks Catastrophic failure Crack propagation range Fionra A Crack Initiation site